The present invention relates to a frequency dividing ratio setting device for programmable counters.
There has been widely used the programmable counter to frequency-divide clock pulses supplied corresponding to a value of program terminals. For the purpose of changing the frequency dividing ratio, changeover switches are arranged connected to the program terminals and the program terminal is set to the H or L level by the switching operation of the changeover switch. Or an up/down-counter is arranged to supply output signals to the program terminals.
However, it is troublesome to change the frequency dividing ratio in the case of changeover switches employed, and it is also unpractical to use changeover switches because the number of changeover switches increases as the frequency dividing ratio becomes larger. Further, in the case where a local frequency is provided in the synthesizer-receiver of PLL type, for example, to set the frequency dividing ratio using the output signal of the up/down-counter, the following disadvantage occurs. Namely, a channel band for AM band is 9 KHz in Japan and the frequency dividing ratio of programmable counter must be a multiple of 9. Therefore, it must always be checked whether or not the content of the counter has reached a multiple of 9, thus making it necessary to add a circuit. In addition, the additional circuit will be very complicated.